1. Field of the Invention
This invention relates to a process for compacting and solidifying various solid waste materials to effect the volume reduction thereof simultaneously with the solidification thereof with thermoplastic resins contained in the waste materials and, if necessary, supplementary thermoplastic resins externally supplied thereto, thus facilitating the waste materials for temporary storage or final disposal thereof, to an apparatus for carrying out said process and to an overall system for disposal of the waste materials. The various solid materials include combustibles such as paper towels, rags, working gloves, veneer boards and hampen ropes; incombustibles such as electric cords, aluminum foils and concrete blocks; and others such as plastic-made sheets and ropes, and rubber-made hoses, gloves and boots, the plastics usually comprising at least thermoplastic resins such as PE (polyethylene) and PVC (polyvinyl chloride), and the above waste materials being discharged from homes and factories. The solid waste materials referred to herein also include those, such as ion exchange resins, concrete fragments and insulating materials, which are likely to have been radioactively contaminated due to the use thereof in atomic power plants, and further include harmful heavy metals-containing ion exchange resins discharged from general industrial factories as waste materials.
2. Prior Art
Urban waste materials including various plastics, metals, glass and rubbers discharged from homes and factories, are so-called "combustion-unsuitable waste materials" and they have been disposed of by incineration, landfill or resource recovery. These disposals, however, cause their respective problems or troubles. The various plastics in the waste materials will, in many cases, mainly cause troubles such as clogging of incinerators by molten plastics, damage of the incinerators by local overheating and evolution of harmful gases such as chlorine and dioxin. In case of the landfill disposal, there is much of bulky waste materials such as foamed polystyrene and polyethylene sheets or bags. These bulky waste materials will need high transportation cost and will sometimes come out from underground after once buried in the ground thereby to be blown in pieces by the wind, thus polluting the environments. There have recently been proposed various methods for recovering and exploiting various waste plastics from the viewpoint of effective reuse of resources. In spite of these proposals, however, there is still not overcome the disadvantage that it costs too much to sort urban waste materials since they are composed of various and miscellaneous materials.
There has thus been proposed a method for producing coarse pelletized compacted mixtures by adding particulate inorganic materials (such as sand, rubble, and ashes obtained by incineration) to urban waste materials with aid of thermoplastic resins contained therein (Japanese Patent Gazette No. 57-11273). The method so proposed is still unsatisfactory in that metal pieces, cloths and the like are not pelletized and they are required to be treated after sorting of the urban waste materials.
On the other hand, it has been customary that thermoplastic resin sheets (such as PE and PVC sheets, paper rags, rags, concrete pieces, steel materials, high performance filters, insulating materials, ion exchange resins and the like, which are contaminated with radioactive materials while they are handled in nuclear power plants, are packed in thermoplastic resin bags or else packed therein after the contaminated waste materials have been sorted into combustibles, incombustibles and combustion-unsuitable materials if necessary, after which the bags so packed are encapsulated in drum cans for custody or storage.
As one example, in a case where a comparatively large-sized contaminated waste material such as a high performance filter, composed integrally of wood, filter medium (inorganic material), metal plates and the like, is disposed of, it is necessary to disjoint the waste material and sort the disjointed members thereby disadvantageously making the disposal steps complicated and increasing the possibility of exposing the workers to radioactivity; thus, there has been proposed a specific device for disjointing such a large-sized waste material to prevent the workers from being exposed to radioactivity and facilitate the disposal of the waste material (Japanese Utility Model Gazette No. 59-42720). However, the incombustibles (other than wood) of the disjointed members are destined to be encapsulated in drum cans for storage.
As another example, ion exchange resins are now used for, for instance, purifying condensed water or disposing of waste water in nuclear facilities such as nuclear power plants. The thus used ion exchange resins will raise a problem as to the disposal thereof as waste materials since they are contaminated with radioactivity.
Since, for example, some of the thus used ion exchange resins has radioactivity of as high as 10.sup.1 -10.sup.-2 .mu.Ci/cc and contain Cs and Sr having a long half-life, they must be stored in the safer form for a long time; to this end, there have been researched and developed a method for volume reduction by incineration or wet-type decomposition, and a method for direct solidification with cement, asphalt or plastics, and these methods have already partly been put to practical use. This volume reduction method using incineration, however, will raise a problem that the exchange groups of cation resins of the ion exchange resins decompose to evolve SO.sub.x gas since the ion exchange resins are treated at high temperatures, whereby is raised a problem as to the material of a facility for treating the thus evolved SO.sub.x gas, the recovery thereof and the like. Further, this volume reduction method using wet-type decomposition is disadvantageous in that it not only needs an after-treatment comprising neutralizing SO.sub.4.sup.2- remaining in the decomposed solution with caustic soda or the like and then evaporating the thus neutralized solution for concentration but also needs an expensive decomposing agent for the wet-type decomposition, thus raising a problem as to economy. This direct solidification methods are disadvantageous in that, for example, the volume reducibility is low and the treating facilities are expensive.
On the other hand, such ion exchange resins must be housed or encapsulated as radioactive materials in high integrity containers (HIC) for disposal in U.S.A. for example, even if they are hardly harmful because of their extremely low strength of radioactivity. The HIC, however, is too expensive to be used for encapsulation of ion exchange resins having medium strength radioactivity from the economical viewpoint and, therefore, they are usually stored in tanks and are in few cases subjected to final disposal.
Used ion exchange resins discharged from the general industrial fields (not from nuclear facilities) may easily be dealt with and they are thus recovered and heaped or subjected to landfill. Ion exchange resins containing harmful heavy metals will still raise a problem as to their soil contamination and effluence to rivers and streams when treated for disposal.
The drum cans encapsulating the solid waste materials therein have been stored in storage houses. However, since the unoccupied storage spaces have more decreased than expected, the solid waste materials capable of being burnt are subjected to incineration treatment and then ashes produced by the incineration are stored in drums or solidified with cement to form more stable solids thereof. The said incineration treatment applies to bulky materials such as thermoplastic resin sheets and bags as well as waste paper and it has been widely used for the treatment of solid waste materials discharged from nuclear power plants, radioisotope institutes (RI) and the like.
The incineration treatment is disadvantageous in that when solid waste materials containing plastics in a large proportion are incinerated, a furnace used would be damaged and it is therefore necessary to install a waste gas treating device as an accessory to an incinerator for the incineration treatment, thus producing secondary waste materials from the accessory device and incurring an extra expense for installation of the accessory device.
Further, conventional volume reduction treatments by heating or incineration not only need a specific heat source but also leave a problem to insufficient volume reduction for pressure packing of the volume-reduced waste materials in containers.
Miscellaneous solid waste materials may also be treated for volume reduction by compressing them by a press, and there is being developed a volume reduction device using a high pressure, particularly a surface pressure of about 1000 to 3000 Kg/cm.sup.2. This device will enable thermoplastic resin sheets and bags, paper rags and the like to be compressed almost without gaps left between the materials and, therefore, it provides an effective method for volume reduction. The compressed body obtained by this method is, per se, a non-homogeneous aggregate of miscellaneous waste materials and it is therefore not preferable for a long-term storage.